西藏蛇绿岩地幔中的主要自然金属矿物

SOME NATIVE METALS FROM OPHIOLITIC CHROMITITES IN TIBET

在西藏雅鲁藏布江蛇绿岩带的罗布莎蛇绿岩块的豆荚状铬铁矿床中 ,揭示出一个由 70～ 80种矿物组成的地幔矿物群 ,包括自然金属、合金、硫 (砷 )化物、氧化物和硅酸盐等。这些矿物呈包裹体或脉石产于铬铁矿石中 ,经人工重砂分析 ,自然元素矿物有自然硅、自然铁、自然锌、自然铅、自然铝、自然铬、自然锡、自然镍、自然钨、自然钛、自然锇、自然铱、自然钌、自然钯、石墨、金刚石、自然金和自然银等。文中选择一些自然元素矿物 ,探索这些地幔矿物特点以及蛇绿岩和铬铁矿的形成机制。根据共生矿物群以及罗布莎地幔橄榄岩为新鲜的未蛇纹石化的岩石 ,认为罗布莎自然元素矿物与蛇纹石化作用无关。它们可能是在地核形成时期滞留于地幔中的成核物质 ,抑或是核幔之间化学反应的产物 ,后来被铬铁矿矿浆捕获 ,并同铬铁矿一起由地幔柱作用和板块作用侵位于浅部并仰冲出露于地表。

Some native metal minerals from podiform chromitites of the Luobusha ophiolite in the Yarlong Zangbu ophiolite belt have been discovered, in which about 70～80 types of minerals are present, including native elements, alloys, sulphides, oxides, silicates, and diamonds. These minerals as inclusions are included in the chromitite, which have been collected from separation of a 1 500 kg sample of chromitite, the native element minerals are native silicon, iron, tungsten, lead, aluminum, chromium, tin, zinc, nickel and gold, besides these there are native ruthenium, palladium, silver, osmium, iridium and graphite. Based on these minerals and the mineral assemblage, we suggest that the native element minerals have no relationship with serpentinization in generation, because the mantle harzburgite is fresh and not serpentinized. These native element minerals in the Luobusha chromitites are xenocrysts derived from the deep mantle and were then carried to shallower depths of upper mantle by a rising plume and plate tectonics. They are primary minerals in mantle or core.